METHANE SOURCES AND SINKS IN PADDY RICE SOILS - RELATIONSHIP TO EMISSIONS

Methane sources and sinks in a Louisiana rice soil and how they relate to atmospheric emissions were quantified. Total methane emission from the plant-soil system was compared with methane emission from surface soil between drill rows of rice (Oryza sativa L.), Results showed tha t over 95% of methane emitted to the atmosphere was through the rice p lant. Average emission through the plant-soil system was 300 mg CH4 m( -2) day(-1) and 826 mg CH4 m(-2) day(-1) for the first and ratoon crop s, respectively. By comparison average methane emission from soil betw een drill rows was 2.1 mg CH4 m(-2) day(-1) for the first crop and 12. 7 mg CH4 m(-2) day(-1) for the ratoon crop. Significant methane oxidat ion was measured in the surface oxidized layer in the soil profile bet ween drill rows. Treatment with methylfluoride inhibitor showed that m ethane emission from the soil would be five to ten times greater if ox idation did not occur in the surface layer. Laboratory studies of meth ane oxidation (also using methylfluoride) showed that approximately 30 % of the methane in the rice root rhizosphere was being oxidized by me thanotrophs. Results showed that methane oxidation in the surface oxid ized soil layer and in the root rhizosphere play an important role on limiting atmospheric methane emissions from Louisiana paddy soils.